Ink jet printing is a non-impact method for producing images by the deposition of ink droplets on a substrate (paper, transparent film, fabric, etc.) in response to digital signals. Ink jet printers have found broad applications across markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging. In recent years the drop size of ink jet printers has tended to become smaller and smaller, resulting in higher resolution and higher quality prints. The smaller drop size is accompanied by smaller nozzle openings in the inkjet printhead. These smaller nozzle openings are easier to plug and more sensitive to extraneous deposits which can affect both the size and placement accuracy of the ink jet drop.
The use of ink jets with smaller drop sizes has resulted in a need to maintain the ink ejecting nozzles of an ink jet printhead, for example, by periodically cleaning the orifices when the printhead is in use, and/or by capping the printhead when the printer is out of use or is idle for extended periods of time. The capping of the printhead is intended to prevent the ink in the printhead from drying out. There is also a need to prime a printhead before use, to insure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles and also periodically to maintain proper functioning of the orifices. Maintenance and/or priming stations for the printheads of various types of ink jet printers are described in, for example, U.S. Pat. Nos. 4,855,764; 4,853,717; and 4,746,938. Removal of gas from the ink reservoir of a printhead during printing is described in U.S. Pat. No. 4,679,059. In U.S. Pat. No. 4,306,245 to Kasugayama et al., a liquid jet recording device provided with a cleaning protective means for cleaning and protecting an orifice is described. The cleaning protective means is provided at a reset position lying at one end of the scanning shaft of the device.
With smaller drop sizes, the required cleaning of the ink jet print heads becomes more frequent and takes longer. This results in long printing times, and the cost of the equipment is more expensive. These costs are, in part, a result of the fact that the available ink jet receivers produce a relatively large dot of color for a given ink drop size.
One approach to overcome these difficulties is to use extra inks for light colored areas, in order to hide or make less visible the pattern created by the dots of ink in light colored areas. However, extra inks require more expensive equipment, because additional ink cartridges are needed for the light colored inks. In addition, it is well known to those skilled in the art that strong hue shifts toward muddy colors, particularly in light colors, are caused by having white areas of receiver showing between small dots of colored ink.